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Solar Panel Project Help

Discussion in 'General Electronics Discussion' started by XxAdvancingTechxX, Apr 22, 2013.

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  1. XxAdvancingTechxX

    XxAdvancingTechxX

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    Apr 22, 2013
    I recently ran over a lawn light with a lawn mower, the solar panel and led were salvageable so like any electronic person I wanted to keep it for parts. Now I'm deciding to turn it into a project. I want to turn it into a charger for my phone. The problem is using a voltage meter I found that it was only 1.2 volts and the phone won't charge with less then 5v. So I know I would use a few capacitors to increase voltage, but I am not sure on how to wire that up nor do I know what type of capacitors I should use. I will also need to regulate the charging so it doesn't over charge my phone and I will need to bypass the solar panel as the led goes off in the light. I don't want it to stop charging my phone while there is light lol.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    1) you can't use capacitors (well not capacitors alone) to increase the voltage.

    2) the panel is unlikely to supply enough power to even begin charging your phone, so worrying about overcharge is probably does not need to be your first concern.

    3) the charging circuitry is inside the phone, so it will terminate the charge when the battery is charged.
     
  3. XxAdvancingTechxX

    XxAdvancingTechxX

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    Apr 22, 2013
    So do I need to run a few in series? The panels charge a small battery which then powers thrle LEDs through the night.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Yes, you could run a few in series to increase the voltage, but it's unlikely that you'd get enough current from them.

    I'd expect you'd need a square foot of panel to be able to charge a phone.
     
  5. XxAdvancingTechxX

    XxAdvancingTechxX

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    Apr 22, 2013
    What about if I bout one from radio shack? Its 6 volts and is a rectangle about the size of a flip phone.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Is it designed to charge a phone, or some random batteries?

    A phone expects the charger to be able to maintain (say) 5V at the socket over the range of current the phone demands. This may be around an amp (higher or lower depending on the phone).

    If the voltage sags too much, the phone might simply stop charging. If it rises too high the phone might be damaged.

    A 5W panel is around a square foot in size. Now that's 5W in bright sun, and positioned to be normal to the incident light. Change either of these and you won't get 5W (actually you might not get 5W anyway).

    There is no magic.
     
  7. BobK

    BobK

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    Jan 5, 2010
    Those garden lights generally work by charging an NiMH cell enough to run a 20mA LED for maybe 8 hours. Get 4 of them, let them fully charge the NiMH batteries (this will take about 10 sunny days) then put them in series and you might be able to get about a 1/2 a charge on your phone.

    Bob
     
  8. XxAdvancingTechxX

    XxAdvancingTechxX

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    Apr 22, 2013
  9. dietermoreno

    dietermoreno

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    Dec 30, 2012
    That's brilliant! I want to buy that if it works! Tell me if it works! No more dead phone in summer storms that knock out power!
     
  10. XxAdvancingTechxX

    XxAdvancingTechxX

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    Apr 22, 2013
    Oh it works I have one, but I didn't know if I could make another pretty easy. Apparently not.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    That uses a solar panel to (slowly) charge a battery and then it uses the battery to charge the phone (or whatever).

    So maybe it takes a day of solar charging of the battery to provide 20 minutes of battery charging to the phone.

    Unless you have *much* larger solar panels you will not be able to provide the instantaneous power required to charge a phone, especially in conditions of less than perfect sunshine.

    It's a bit like using a pump to pump up a car tyre. Does your effort go into pumping air into the tyre -- yes, but not directly. You can't easily pusg the air in. However, you can take a large volume of air and over time compress it to a much smaller volume at a higher pressure. Then, for a brief instant, air flows into the tyre. You have to expend maybe a second of effort to get a short (1/4 second?) burst of air into the tyre.

    Likewise the solar panel needs to charge up a battery slowly. It can then be discharged much more quickly into a load which demands more power than the solar panel can provide all at once. But having a phone on for a small fraction of a second isn't useful, so we accumulate the power over hours, an then the phone can draw on that power for minutes.
     
  12. Mongrel Shark

    Mongrel Shark

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    18
    Jun 6, 2012
    You could use a Joule Thief or flyback style blocking oscillator. To boost the 1.2v from the panel up to 5v or more (easy to get a few hundred volts from [email protected]) in a capacitor. Then use a transistor and LED to discharge the cap in pulses to the battery. The Led gives a voltage differential before the transistor turns on, then there is a path of lower resistance, and the cap drains to battery voltage. at which point the transistor switches off, and the cap fills again. I can do thin in frequency from a few hundred hertz, to hundreds of kilohertz. Depending on rate of power supply. Ie it goes slower on less input power. Or its possible to charge, just putting the inductor pulse output directly across the battery too. Still testing to see which way is most efficient.

    Its not perfect. and still in experimental stages. I have been playing with this system with many batterys for a few months now. I can take a little more amps, at a lower voltage and give a 12v lead acid a maintaining trickle charge this way. and am getting good results from AA's C's D'c etc As well as my home made lead alum batterys. Most batterys seem to respond well to this type of charge. Problem is your Phone and battery have inbuilt charge controllers that wont let it work. You can get DC 5v no worries. but the amps is pathetic. Probably want do much charging, if it does it will be really slow. I have seen other people charge LI-po and Li-ion this way, but they normally take the battery out of the device, and cut it open to remove the controlling circuitry. Not advisable if you dont know exactly what you are doing. Li-po's can burst into flame or even explode. If over charged.


    Up side is, if you get it right, you can charge and recover batterys that have done many cycles and no longer charge. I have recovered Ni-cd's and Ni-mh this way. So they charge on comercial chargers that previously rejected them. I have seen similar things done with lead acid and various lithium cells. Its tricky getting a decent efficiency though.

    It is do-able, but its a bit advanced. Not for beginners.

    I'm working on a device that will charge Phones and MP3's etc, via USB from flat disposables, or ambient (or direct) sunlight. I will likely be incorporating some batterys in the device though. To store up the "harvested" power, for solid dc output to a device to be charged, without modifying the device..

    There are 5v panels on ebay that will do what you want. Some even have internal batterys, so you can save some charge for after dark.
     
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